Valve trains of internal combustion engines have a variety of components depending on the design of the engine, however, most modern valve trains have a valve with its associated valve stem, a hydraulic lash adjuster and a cam which actuates the valve through the valve stem.
Hydraulic lash adjusters need oil to function. Hydraulic lash adjusters have a low pressure cavity that acts as an oil reservoir and a high pressure cavity that is fed oil through a check valve positioned between the low pressure and the high pressure cavities. Typically, oil is fed to the hydraulic lash adjuster either through an inlet in the side wall or through an inlet in the top wall of the hydraulic lash adjuster. The inlet of the hydraulic lash adjuster is in fluid communication with the low pressure cavity. The inlet in the side wall is fed oil from a conduit within the engine while the inlet in the top wall is usually fed through a rocker arm. In certain configurations, the rocker arm feeds oil to the hydraulic lash adjuster by means of a hollow push rod.
In overhead cam engines with rocker arms, the cam operates on one end of a rocker arm while the other end of the rocker arm has a hydraulic lash adjuster which is mounted on the top of the valve stem. In such an arrangement, the rocker arm can be mounted on a hollow rocker arm shaft which has a bore therein for carrying oil to the rocker arm. The rocker arm also has a bore in fluid communication with the rocker arm shaft bore. The hydraulic lash adjuster is fed oil through various inlets and outlets in the rocker arm shaft bore and the rocker arm bore such that oil travels to the low pressure cavity of the hydraulic lash adjuster.
In overhead valve engines, the hydraulic lash adjuster is in contact with the cam and a hollow push rod is positioned between the top of the hydraulic lash adjuster and the rocker arm. The other end of the rocker arm is in contact with the valve stem. The hydraulic lash adjuster receives oil through the rocker arm shaft bore, the rocker arm bore and the push rod bore. The push rod bore being in fluid communication with the top inlet of the hydraulic lash adjuster, thereby feeding oil to the low pressure cavity.
In each of these arrangements, the hydraulic lash adjuster is the end of an oil passageway and metal particles which are contained within the oil can collect in the hydraulic lash adjuster and cause failure of the hydraulic lash adjuster. Such failure usually occurs when the metal particles find their way from the low pressure cavity to the high pressure cavity and jam the moving mechanisms of the hydraulic lash adjuster. Typically, these metal particles are iron or ferrous in nature. These iron particles come from machining which is done to the engine during manufacture as well as wear of the various parts in the engine.
To date, filters or screens have been positioned in the hydraulic lash adjuster to prevent the iron particles from contaminating or damaging the workings of the hydraulic lash adjuster. These filters and screens can become clogged and in certain situations are unsuitable for use in the hydraulic lash adjuster because the size of the low pressure cavity in the hydraulic lash adjuster is too small to accommodate the screens.